The present invention relates to a transmission equipped with an auxiliary speed changing gear.
The transmission of the kind mentioned above is usually used in such a heavy-duty vehicle having an engine the output power of which is relatively small for the heavy load of the vehicle, in order to ensure a sufficiently high running performance of such vehicle.
Most ordinary construction of the transmission of this type has a main transmission the gear ratio of which can be changed over 3 to 5 stages, and auxiliary speed changing gear of 2 to 3 stages and connected in series to the main transmission. Various types of auxiliary speed changing gears have been known such as those incorporating planetary gears or counter gears.
However, in the conventional transmissions having an auxiliary speed changing gear, the weight of the transmission as a whole, as well as the space occupied by the transmission, is impractically large, because the auxiliary speed changing gear and the main transmission are arranged and installed independently of each other.
At the same time, the cost of the transmission as a whole is considerably high, as compared with the commonly used transmission having no auxiliary transmission.
For these reasons, the transmission having an auxiliary speed changing gear could not be successfully used in small vehicles such as passenger cars, due to the restrictions in weight, size and cost, although it has been practically used in large size heavy-duty vehicles for industrial purposes.
In order to make the minimized fuel consumption rate and the sufficiently high running performance compatible with each other, over various running modes including expressway-cruising, running across traffic snarl in the street, hill-climbing and downing in the mountainous areas, the number of speed changing ratios to be performed by the transmission has to be as large as 6 to 10. The shifting operation with the transmission having such a large number of speed changing ratios is extremely troublesome.
In case of passenger cars, the output power of the engine is sufficiently large, so that the transmission gear may be shifted at each two stage, i.e. skipping over the adjacent stage.